A proposed fuel cell system includes: fuel cells that generate electric power through electrochemical reactions of oxygen included in an oxidizing gas, which is flown through oxidizing gas conduits provided on a cathode side of respective electrolyte membranes, with hydrogen included in a fuel gas, which is flown through fuel gas conduits provided on an anode side of the electrolyte membranes; piezoelectric elements that are located in the oxidizing gas conduits and are displaced by a driving voltage; and vibrators that are also located in the oxidizing gas conduits and vibrate with the displacement of the piezoelectric elements (for example, see Patent Laid-Open Gazette No. 2002-184430). In this fuel cell system, water produced by the electrochemical reactions on the cathode side may be flocculated to water droplets and prevent the smooth flow of the oxidizing gas. In such cases, the piezoelectric element is displaced to trigger vibration of the vibrator. The vibration atomizes the water content on the surface of the cathode, thereby removing the water content.
This prior art fuel cell system is, however, required to locate the piezoelectric elements and the vibrators functioning as the movable members in the restricted space of the gas conduit. This undesirably complicates the structure. Another problem is that atomization of the water droplets flocculated in the gas conduits may take a relatively long time.